1. Field of the Invention
The present invention relates generally to testing tools for echo canceller systems in communication networks. More particularly, the present invention relates to methods and systems for automated testing of echo cancellers using natural speech excitations.
2. Background Art
Subscribers use speech quality as the benchmark for assessing the overall quality of a telephone network. A key technology to provide a high quality speech is echo cancellation. Echo canceller performance in a telephone network, either a TDM or packet telephony network, has a substantial impact on the overall voice quality. An effective removal of hybrid and acoustic echo inherent in telephone networks is a key to maintaining and improving perceived voice quality during a call.
Echoes occur in telephone networks due to impedance mismatches of network elements and acoustical coupling within telephone handsets. Hybrid echo is the primary source of echo generated from the public-switched telephone network (PSTN). As shown in FIG. 1, hybrid echo 110 is created by a hybrid, which converts a four-wire physical interface into a two-wire physical interface. The hybrid reflects electrical energy back to the speaker from the four-wire physical interface. Acoustic echo, on the other hand, is generated by analog and digital telephones, with the degree of echo related to the type and quality of such telephones. As shown in FIG. 1, acoustic echo 120 is created by a voice coupling between the speaker or the earpiece and microphone in the telephones. For a speakerphone, for example, the sound from the speaker is bounced off the walls, windows, and the like and is picked by the microphone. Similarly, an acoustic coupling can also happen in conventional or in wireless telephone handsets. The result of the hybrid echo and/or the acoustic echo reflections is the creation of single-path or multi-path echo, which would be heard by the talker unless eliminated.
As shown in FIG. 1, in modern telephone networks, echo canceller 140 is typically positioned between hybrid 130 and network 150. Generally speaking, echo cancellation process involves two steps. First, echo canceller 140 employs an adaptive filter to model hybrid echo 110 (and/or acoustic echo 120 if it exists). The adaptive filter adapts to create a model of echo signals, based on far-end signal 142 and local-end signal 132, which includes the echo signal of far-end signal 142 generated by hybrid 130. Far-end signal 142 is filtered by the adaptive filter to generate a model of echo generated by echo sources 110 and 120, and is subtracted from local-end signal 132 to generate a residual echo signal. Although this echo cancellation process removes a substantial amount of the echo, non-linear components of the echo may still remain in the residual echo signal. To cancel non-linear components of the echo, the second step of the echo cancellation process utilizes a non-linear processor (NLP) to eliminate the remaining or residual echo by attenuating the signal below the noise floor, and to generate output signal 144.
Because performance of echo cancellers is one of the key elements for ensuring network quality, various standards have been adopted for defining minimum echo canceller operating requirements. These standards are typically used as a benchmark for testing and selecting echo cancellers. A noteworthy standard is known as ITU-T (International Telecommunication Union-Telecommunication standardization sector) G.168, entitled “Digital Network Echo Cancellers”, dated August 2004, which is hereby incorporated by reference in its entirety. Another standard is known as ITU-T P.831, entitled “Subjective Performance Evaluation of Network Echo Cancellers”, dated December 1998, which is hereby incorporated by reference in its entirety.
However, it is well known that simply complying with G.168 or P.831 tests does not guarantee adequate echo cancellation performance outside a laboratory or testing environment. In fact, ironically, an echo canceller may fail G.168 or P.831 compliance test, but perform more effectively outside a laboratory or testing environment than some echo cancellers that pass the compliance test. This is because of many inherent drawbacks in the existing G.168 or P.831 compliance tests. For example, the automated objective tests of G.168 use artificially generated synthetic excitation and limited echo canceller operating scenarios due to the limitations of the automated measurements, and therefore the test results do not fully correlate with the performance of echo cancellers in a wide range of real-life operating scenarios. On the other hand, the manual subjective tests of P.831 are limited in scope and require live participants and statistical inferences, and can be quite expensive and time consuming.
Accordingly, there is a need in the art for a new approach to echo canceller compliance tests that can more accurately and effectively benchmark echo cancellers' performance under real-life conditions with less human interaction and costs.